This invention relates to an antiskid control device which monitors movements of a vehicle's wheels under braking conditions and minimizes the braking range for stopping the vehicle.
Japanese Laid-open Patent Application No. 61-98663, published without examination on May 16, 1986, discloses an antiskid control device known prior to the present invention. This device comprises a pair of diagonal hydraulic pipe-lines connecting diagonally positioned front and rear brakes on a vehicle, a pair of pressure controllers responsive to the movements of the front wheels preventing the front wheels from locking, and hydraulic pumps driven by rotation of the front wheels for supplying hydraulic pressure to the rear brakes through the pipe-lines.
According to this prior art, the hydraulic pressures to the rear brakes are generated by the pumps in response to the rotational speeds of the corresponding front wheels. Therefore, the hydraulic pressures to the rear brakes are defined by the respective rotational speeds of the corresponding front wheels. Consequently, when the hydraulic pressures to the front wheels are controlled by the pressure controllers, the hydraulic pressures to the rear brakes are also controlled. Therefore, in this prior art, the coefficients of friction between each of the front and rear wheels and a road surface may be utilized efficiently. Thus the braking range for stopping the vehicle can be shortened.
In the conventional; antiskid controlling device, however, the directional stabilization of the vehicle is not consistent with the minimizing of the braking range for stopping the vehicle. Therefore, even if the antiskid controlling device is performing normally, the vehicle may turn left or right suddenly at times against the driver's steering force.
For example, when the vehicle runs on a road where there is packed snow under the right wheels and dry asphalt under the left wheels, if the conventional antiskid control device starts its operation, the front left wheel generates a higher braking force than the front right wheel. Therefore, even if the conventional antiskid control device operates normally, a yawing moment causing the vehicle to turn left may be generated by the difference of the braking forces between front right and front left wheels.
Such yawing moment may be cancelled if a driver steers the vehicle in a proper steering manner. Under normal driving conditions, however, it is difficult for a typical driver to react and to steer the vehicle in the proper manner quickly. Therefore, when the vehicle runs at high speed, it is preferable for the vehicle driver to control the hydraulic pressures to the brakes in order to prevent any yawing moment from being generated.
When the vehicle runs at low speed, even if a yawing moment is generated, the turning of the vehicle can be avoided by manually steering the vehicle against the yawing force. Accordingly, when the vehicle runs at low speed, it is preferable for the vehicle driver to control the hydraulic pressures to the brakes in order to shorten the braking range by utilizing the braking force efficiently.